Textured fingers for precise temperature adjustment of preheated parison preforms

ABSTRACT

Tubular parison preforms for blow molding generally oval-shaped oriented hollow articles such as bottles are reheated to orientation temperature and the sides of the parison which are to be expanded out along a major axis of a mold are contacted with textured fingers so as to lower the temperature a very small amount. This allows the portion of the parison corresponding to the major axis of the mold to resist stretching and thus compensates for the unequal wall thickness which otherwise results when the parison touches the walls of the mold opposite the minor axis and is thereby chilled.

United States Patent [191 Hudson et al.

TEXTURED FINGERS FOR PRECISE TEMPERATURE ADJUSTMENT OF PREHEATED PARISONPREFORMS Inventors: Jimmie E. Hudson, Bartlesville,

' Okla.; Jimmy W. Snelson, Orangeburg, N.Y.

Phillips Petroleum Company, Washington, DC.

Filed: Apr. 10, 1972' Appl.No.: 242,385

Assignee:

us. Cl. 425/387 B, 425/384 Int. Cl 829d 23/03 Field ofSearch 425/DI G.208, DIG. 213, MW 42 5/DIG, 214, 425/DIG. 216, 387 B, 342, 284

References Cited UNITED STATES PATENTS 3/1957 Sherman 425/DIG. 213

[451 Feb. 5, 1974 3,000,051 9/1961 Schaich 425/DlG, 213 r 3,125,6193/1964 Miller 425/326 13 3,283,046 11/1966 Dewitt et a1. 425/DIG. 208

Primary Examiner-Richard B. Lazarus Attorney, Agent, or Firm-Quigg andOberlin [5 7] ABSTRACT Tubular parison preforms for blow moldinggenerally oval-shaped oriented hollow articles such as bottles arereheated to orientation temperature and the sides of the parison whichare to be expanded out along a major axis of a mold are contacted withtextured fingers so as to lower the temperature a very small amount.This allows the portion of the parison corre- 'ie n ia t q film ier axit hq mold to resist stretching and thus compensates for the unequal wallthickness which otherwise results when the parison touches the walls ofthe mold opposite the minor axis and is thereby chilled.

6 Claims, 5 Drawing Figures PAIENIEUFEB 51974 w ml iv y w wt BACKGROUNDOF THE INVENTION This invention relates to blow molding oriented hollowarticles of irregular shape from reheated parison preforms.

While patents in the blow molding art go back over 100 years, it hasbeen only in the last years or so that blow molding of hollow plasticarticles has achieved significant commercial success. Blow molding hastraditionally been associated with the formation of bottles of agenerally round configuration. In recent years, however, there have beenefforts to expand the blow molding techniques to encompass the formationof more sophisticated moldings, including such diverse items as hollowbeverage cases having integral dividers and items having integrallymolded handles, and the like. With'conventional blow molding techniquesutilizing a thoroughly molten parison it is a fairly simple matter tocompensate for an unsymmetrical configuration of the final product byeither of several means. First, the extrusion of the parison can beprogrammed to give annular areas of greater thickness or a flattened dieor bushing can be utilized to give a longitudinal thick section orsections in the parison. In addition, a perfectly cylindrical parisoncan be extruded and chilled by means of blowing air thereon orcontacting 'with a smooth metal surface to chill the parison from itsmolten condition to a much lower temperature at which the viscosity isgradually increased. Such a technique is shown in MillerUS. Pat. No.3,125,619, for instance. Forming oriented articles from individualcylindrical parison preforms reheated to their orienting temperature,however, presents a different situation. It is virtually impossible toextrude the initial parison preform with the appropriate variations inwall thickness because of the difficulty of indexing these thicker andthinner areas in the final molding operation. Also, there is only arelatively small part of a short arc around the tube which is affectedand grossly uneven parisons do not blow predictably. Utilizing smoothsurfaced cooling fingers presents a problem in that the parison atorientation temperature is so extremely sensitive to minor temperaturevariations that it is in some instances virtually impossible to provideapparatus which can mechanically contact the parison and retract thecooling fingers quickly enough to prevent the parison from being cooledto a sufficiently crystalline state that it cannot be molded properly inthe cooled areas.

SUMMARY OF THE INVENTION It is an object of this invention to provideirregularly shaped biaxially oriented hollow articles having wallsections of improved uniformity; it is a further object of thisinvention to provide an apparatus suitable for selectively adjusting thetemperature of a reheated parison preform at orientation temperature;and it is yet a further object to selectively adjust the temperature ofa reheated parison preform at orientation temperature.

In accordance with this invention tubular parison preforms are heated toorientation temperature with at least one side portion thereofcorresponding to a major axis of the article to be molded beingcontacted subsequent to said heating but prior to said molding with atextured temperature adjustment finger.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, forming a parthereof, wherein like reference characters denote the like parts in thevarious views,

FIG. 1 is a schematic representation of a blow molding operationutilizing the textured fingers of the invention; 1

FIG. 2 is a detailed front elevation of a textured temperatureadjustment finger;

FIG. 3 is a view along section line 3-3 of FIG. 2;

FIG. 4 is across sectional'view of an oval-shaped mold with acylindrical parison disposed therein prior to blowing; and

FIG. 5 is a perspective view of fingers in accordance with analternative embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention is applicable-tothe formation of any irregularly shaped biaxially oriented blow moldedarticle at least a portion of which has a major axis of at and bottleshaving a conventional round shape at the top with an oval'section at thebottom. Also it is intended to cover articles which are not symmetrical,that is, articles having a bulge on one side, in which case only thatone side of the parisonwhich would correspond to this bulge would becontacted with thetextured temperature adjustmet fingers.

The invention is applicable to the production of these articles from anyorientable plastic material. Exemplary polymers from which theseparisons can be made are orientable cyrstalline materials such aspolyesters and polymers of at least one mono-l-olefin having 2-8 carbonatoms per molecule and oriented amorphous materials such as poly(vinylchloride), polystyrene, butadiene-containingpolymers and styreneacrylonitrile-containing polymers. Preferred polymers are polymers andcopolymers of ethylene, propylene, and butene, particularlypolypropylene. The invention is of particular utility with copolymers ofpropylene anda minor amount of ethylene, having a melt flow of one tothree, preferably about two as measured by ASTM D l238-62T, condition L,and a densityof 0.900 to 0.905 a as measured by ASTM D l505-63T.

These polymers can be formed into hollow parison preforms by simpleextrusion of a pipe which is thereafter severed into individual lengthsorby injection molding or by other conventional techniques. Theresulting tubular parison is thereafter cooled to ambient temperatureand stored preparatory to being heated to orientation temperature.

In the case of crystalline polymers, the orientation temperature towhich they are reheated is generally in the range of l to 50, preferably10 to F below the crystalline melting point. Amorphous polymers have anorientation temperature generally to 225, preferably 100 to 175F belowthe homogeneous melt point. Thus the preferred propylene copolymerswould preferably be heated in an air oven at a temperature of about295-320, preferably 305308F with the parison coming to a temperature ofabout 5F below the oven temperature.

After the parison has been reheated to orientation temperature theportions corresponding to the major axis of the mold (or the singleportion in the case of a bulged asymmetric article) are contacted withthe textured temperature adjustment fingers so as to reduce thetemperature in the area of contact by an amount within the range of 0.25to 10, preferably 0.5 to 5, more preferably O.5 to 2F below that of therest of the parison but still within the orientation range. Of coursethere may be some temperature gradient through the wall of the parisonand'all of these figures are meant to refer to average temperatures.

The textured fingers in accordance with the inventions must have asubstantial texture which can be imparted by the use of a series ofgrooves in the form of a cross hatch, square, or diamond pattern forinstance. Mere sandblasinting to get a slightly textured surface is notsufficient. Preferably the grooves are at least one thirty-second of aninch deep, preferably one thirtysecond to one-eighth of an inch, morepreferably one thirty-second to one-sixteenthof an inch. The groovesshould be spaced so that about 40 to 60, preferably about 50 percent ofthe surface constitutes the lands, and the other portion of grooves.

The textured temperature adjustment fingers of the instant invention canbe made of any suitable structural material. Particularly suitablematerials are aluminum or brass.

In a more specific embodiment of the invention, instead of using asingle textured temperature adjustment finger on each side, a series ofparallel fingers are used which allows even more precise adjustment ofthe temperature to point only a fraction of a degree below that of thesurrounding material.

Referring now to the drawings, particularly FIG. 1, there is shown inschematic representation a blow molding apparatus utilizing the texturedtemperature adjustment fingers of the instant invention. Extruder formsa tubular extrudate 12 which passes to cooling and sizing zone 14 andthence to cutting means 16 where it is cut into individual open endparison preforms 18 which fall into loading hopper 20 of oven 22. Oven22 is a circulating air oven having a continuous chain 24 withv parisonsupport means 25 for conveying parisons l8'therethrough in an uprightmanner.

Parison transfer mechanism designated generally by reference character28 transfers the parisons from oven 22 to the molding station generallydesignated by reference character 30. At the point in the cycledepictedin FIG. 1, gripping means designated generally by referencecharacter 32 has grasped the outer end of the parison by means of clampmembers 35. Textured temperature adjustment fingers 26 are shownpreparatory to being closed onto the sides of parison 18 correspondingto the major axis of the resulting article. Contact time between fingers26 and the parison is generally'as short as it is mechanically feasibleto provide. Generally, this contact time will be within the range of0.001 to 1 second, preferably 0.1 to 0.5 second. Thereafter grippingmeans 32 is moved into position above molding station 30 and lowered topositionto bottom open end of parison 18 over thread-forming plug 38.Thread-forming jaws 40 then close and optionally plug 38 is advancedaxially upward an additional distance into theopen end of said parisonto thus form the thread and/or neck area. Gripping means 32 then movesaxially upward again, thus stretching the parison between threadformingjaws 40 and clamp members 35. This stretching operation terminates justas the gripping means clears above the top of mold halves 42 and 44.Mold halves 42 and 44 then converge with leading edges 46 of said moldhalves severing the parison which is sealed adjacent thereto. Fluidpressure is then introduced via line to expand said parison intoconformity with the mold cavity to form a biaxially oriented bottle.During this time gripping means 32 is raised to its uppermost height androtated into position over a scrap receiving means wherein clamp members35 open to deposit the severed end of parison 18. Additional rotation oftransfer mechanism 28 brings it over oven 22 preparatory to beinglowered to grasp another parison, etc. Members 26 could, of course, bepositioned so as to contact parison 18 at the point at which member 32has transferred to parison into position just above molding station 30preparatory to lowering same.

The above operations are carried out sequentially so that the parisonremains at orientation temperature during the stretching and blowing.

The mold halves then open and the thus formed bottle .is removed. Plug38 is moved axially upward'and downward by'means of cylinder '39. Jawmeans 40 are moved into and out of engagement with the parison by meansof cylinder 41 and mold halves 42 and 44 are opened and closed by meansof air cylinder 43. Air is introduced into the interior of the parisonto effect expansion of same via line 45 which feeds into a hollow coreof plug 38.

Now referring to FIG. 2, there is shown a front elevation in detail of atemperature adjustment finger 26 showingcross hatch grooves 48. In theembodiment shown the finger is about three-sixteenths of an inch wide atthe top and one-half inch wide at the bottom with the overall heightbeing 1% inches. Ofcourse, the size and shape can be varied to fit theindividual article being molded. Generally the articles being moldedwill have a greater difference between the length of the major and minoraxis near the middle and bottom thereof because generally the neck willbe round or generally round.

FIG. 3 shows a sectional view of temperature adjustment finger 26showing means to move said fingers quickly into and out of engagementwith the parison. Means 50 can be a pneumatic cylinder or the like.Finger 26 is shown with a radius corresponding to the radius of theoutside diameter of the parison. Generally each finger 26 will encompassabout one-fourth of the circumference of the parison although this canbe varied to fit individual applications.

Referring now to FIG. 4. there is shown parison 18 which has beencontacted by temperature adjustment fingers 26 along portion Acorresponding to wall 52 at the end of the major axis of the mold cavityand along portion 8 corresponding to wall 54 also along the major axisof the mold cavity. Thus on introduction of internal fluid pressureportions Aand B will resist expansion to a very slight degree and thuscompensate for the reduced stretching normally encountered when theparison contacts the walls at the ends of the minor axis of the mold. Itis to be emphasized that the amount of tempera-ture adjustment must bekept very small; otherwise since the polymer is at orientationtemperature, it will simply be cooled below the point at which it willstretch significantly which gives an entirely unsatisfactory molding.

FIG. 5 shows an alternative embodiment of the invention whereintemperature adjustment fingers 26a comprise a plurality of parallelmembers which further facilitates achieving more precise adjustment ofthe temperature a matter of a fraction of a degree or at the most acouple of degrees Fahrenheit.

It must be kept in mind that, at the temperatures in question, thepolymer exhibits elastic as opposed to plastic characteristics and onlysmall fluctuations in temperature can have disastrous effects on theresulting molded article. That is if there is substantial cooling, thecooled portion will not stretch at all and conversely substantialheating of a particular area will result in either the article blowingout and forming a hole in this point or at least achieving nosignificant orientation. It is to be further emphasized that theuniformity obtained in accordance with the invention relates to morethan just a simple maintaining more nearly even wall thickness, althoughthat is important. By achieving substantially even stretching of allportions of the material, it is possible to achieve orientation in allportions of the parisons and this has a dramatic effect on strength. Forinstance, in a conventional blow molding operation utilizingtemperatures where the polymer is thoroughly molten, a difference intemperature of as much as 100F may have only a slight effect on theviscosity, with a resulting slight effect on the resulting wallthickness; for the most part strength would be increased an amountproportionate to the increase in wall thickness. However, operating inaccordance with the invention, achieving uniform orientation allowsmorecomplete advantage to b'e taken of the orientation effect whichincreases the strength a factor of or more over the strength ofunoriented material.

Generally the members shown in FIG. 5 will be disposed in a parallelrelationship relative to the longitudinal axis of the bottle.

Many conventional parts such as temperature controllers, thermostats,frame members and the like have been omitted from the drawings for thesake of simplicity, but their inclusion is understood by those skilledin the art and is within the scope of the invention.

CALCULATED ILLUSTRATIVE EMBODIMENT A predominantly propylene copolymerhaving a small amount of ethylene therein with a density of 0.902 (ASTMD 1505-63T) and a melt flow of two (ASTM D l238-62T), condition L, and acrystalline melting point of about 320F is extruded into tubing havingan outside diameter of 1.345 inches and a wall thickness of 0.175 inch.The tubing is cooled to room temperature in a vacuum sizing quenchingchamber and cut into 6-inch work pieces. These 6-inch lengths are placedin a heatingoven such as is shown in FIG. 1, which oven is adjusted to atemperature of 305308F. After about 45 minutes the parisons are removedfrom the oven and contacted with two temperature adjustment fingers suchas are shown in FIG. 2 for a time sufficient to adjust the temperaturein the area contacted to an average of about lF below that of the restof the parison. Each finger is threesixteenths of an inch wide at thetop, one-half inch wide at the bottom and 1% inches long. The parison isthen transferred immediately into position in a molding zone andexpanded by internal fluid pressure to give a bottle having a generallyround upper neck area and an oval to rectangular body portion as shownin FIG. 4 having an average width along. the major axis of the resultingarticle of about 4% inches and an average width along the minor axis ofthe resulting article of about 1% inches. The resulting article issevered along a plane perpendicular to the long axis of the bottle at apoint along the widest dimension of the generally oval to rectangularbody portion. The walls opposite the major axis are about one-half thethickness of the walls opposite the minor axis. No extremely thin orthick areas are found.

CONTROL Identical polymer to that of the calculated illustrativeembodiment was formed into identical parisons and treated in identicalmanner except the sides were contacted with smooth surfaced coolingfingers. The resulting bottle had two lumps corresponding to the areastouched by the smooth surfaced cooling fingers. Contact time was reducedto the smallest level mechanically possible on a commercial scalemachine with the same results with this'particular polymer although itwas possible to obtain reasonably satisfactory results with somepolymers utilizing a smooth surfaced cooling finger.

While this invention has been described in detail for the purpose ofillustration, it is not to be construed to be limited thereby but isintended to cover all changes and modifications within the spirit andscope thereof.

We claim: I

1. Apparatus comprising in combination a tubular parison heating means;

plug means adapted to be inserted into one end of said tubular parison;

jaw means, and means to open and close said jaw means, said jaw meansbeing adapted to cooperate with said plug means to form a neck finish onsaid one end of a parison;

gripping means adapted to grip an endof a parison and transfer same fromsaid heating means into position over said plug, said gripping meansbeing adapted to move axially away from said plug and jaw means aftersaid jaw means have closed;

at least one textured temperature adjustment finger adapted to contactsaid parison after said gripping means has removed same from saidheating means, and means to move saidat least one textured temperatureadjustment finger into and out of engagement with atleast one side ofsaid parison; and

a generally oval mold cavity means at least a portion thereof having aratio of a major to minor axis of at least 1.25 to 1, said mold cavitymeans being disposed relative to said at least one textured temperatureadjustment finger and said gripping means such that said side of saidparison engaged by said at least one textured temperature adjustmentfinger corresponds to said major axis of said mold.

. 2. Apparatus according to claim 1 wherein said at 5 least one texturedtemperature adjustment finger comprises a pair of opposed members.

3. Apparatus according to claim 1 wherein said at least one texturedtemperature adjustment finger has 8 5. Apparatus according to claim 3wherein said at least one textured temperature adjustment finger is madeof aluminum metal. 6. Apparatus according to claim 1 wherein each ofsaid at least one textured-temperature adjustment finger comprises aplurality of parallel members.

1. Apparatus comprising in combination a tubular parison heating means; plug means adapted to be inserted into one end of said tubular parison; jaw means, and means to open and close said jaw means, said jaw means being adapted to cooperate with said plug means to form a neck finish on said one end of a parison; gripping means adapted to grip an end of a parison and transfer same from said heating means into position over said plug, said gripping means being adapted to move axially away from said plug and jaw means after said jaw means have closed; at least one textured temperature adjustment finger adapted to contact said parison after said gripping means has removed same from said heating means, and means to move said at least one textured temperature adjustment finger into and out of engagement with at least one side of said parison; and a generally oval mold cavity means at least a portion thereof having a ratio of a major to minor axis of at least 1.25 to 1, said mold cavity means being disposed relative to said at least one textured temperature adjustment finger and said gripping means such that said side of said parison engaged by said at least one textured temperature adjustment finger corresponds to said major axis of said mold.
 2. Apparatus according to claim 1 wherein said at least one textured temperature adjustment finger comprises a pair of opposed members.
 3. Apparatus according to claim 1 wherein said at least one textured temperature adjustment finger has grooves having a depth of one thirty-second to one-eighth inch.
 4. Apparatus according to claim 3 wherein said grooves occupy 40-60 percent of a contact surface of said at least one textured temperature adjustment finger and lands therebetween comprise the remaining portion of said surface.
 5. Apparatus according to claim 3 wherein said at least one textured temperature adjustment finger is made of aluminum metal.
 6. Apparatus according to claim 1 wherein each of said at least one textured temperature adjustment finger comprises a plurality of parallel members. 